Gaseous and particulate emissions.

Abstract:

The need to limit sulphur dioxide, nitrous oxides and particulate matter emissions
from fossil fuel combustion processes is now a major factor in the design,
construction and operation of plants. Over the past 5 to 10 years, most developed
countries have introduced legislations to control these. emissions. This report was
done to investigate emissions of sulphur dioxide (S02), nitrogen oxides (NOx) and
particulate matter from coal fired power plants.
S02 emissions contribute to an air pollution load that has been found to be linked to
respiratory and heart problems. It increases the formation of acid precipitation, called
acid rain. NOx oxides to nitrogen dioxide (N02). N02 acts as an irritant to the
respiratory tract, alveoli of the lungs and causes chest pains. Toxic elements
concentrate on fine particulate matter because of their high surface-area to volume
ratio. These particles penetrate and settle onto the lung wall, leading to respiratory
disorders and lung diseases.
Due to the strict legislative requirements, flue gas detoxification processes were
investigated. They include:
• Wet scrubbing
• Spray dry scrubbing
• Dual-alkali
• Well man-Lord
• Activated carbon
• Magnesium oxides
• Selective catalytic recovery
• Circulating fluidised bed combustion
• Electromembrane desulphurisation
A study was done to show the possible cost implications associated with the wet
scrubbing, spray dry scrubbing, selective catalytic recovery, circulating fluidised bed
and electromembrane desulphurisation process. A variety of methods were used to
calculate cost, due to costs being difficult to obtain. Most of the information was
based on European, Asian and American installations. The objective of this
economic analysis was to compare the different technologies. Because of the
assumptions used, costs were always "order of magnitude" estimates. Capital and
operating costs were calculated for these technologies, but they can only be used as
an indication of costs and to allow for comparisons between the technologies. The
costs were converted using the January 2000 exchange rates. Due to this, costs
may be more inflated than what would normally be expected due to equipment being
purchased earlier than January 2000. Of the processes investigated, the circulating
fluidised bed process was found to be the most economical. There is no inexpensive route for the removal of sulphur dioxide, nitrous oxides and
particulate matter. The most suitable detoxification process will depend on the
legislative requirements per country. South Africa is a signatory of the Montreal
Protocol and the Framework for Climatic Change. Legislations for gaseous
emissions were not considered a priority. Currently, Eskom's drive is to electrify
townships rather than spend money on detoxification processes. However, future
legislations may require more stringent control measures.